1. Field of Invention
This invention relates to conveyor type rollers including those submerged in the zinc-pot of a galvanizing line. The bearings of these rollers are designed to minimize the torque required to keep them turning by the friction between the roller surface and roller driving belt or sheet. When such a roller stalls, the resulting damage to the conveying belt or sheet, especially in steel galvanizing lines, is a major concern. This invention discloses an alternate roller bearing/shaft configuration capable of reducing bearing friction torque as well as extending the life of the bearings.
2. Background
Rollers used on conveyors and inside the zinc-pot of a steel-sheet galvanizing line are usually driven only by friction between the roller and the belt or sheet. Bearing friction torque and associated wear depends mostly on: roller load, roller weight, contacting bearing materials, their surface finish and bearing diameter. Most important for bearing wear rate are: bearing materials, lubrication, temperature, velocity, average contact pressure and degree or clearance and roundness of the bearing sleeve inside each bearing housing. Bearing wear rate increases dramatically with miss-alignment of the bearing housings and with shaft deflection. The allowable bending stress in the shaft, limits the bearing diameter (D) and length (L). Rollers operating in high temperature furnaces or in a hot zinc-pot of a steel galvanizing line often have negligible lubrication. In such cases, bearing life may be limited to only one week of operation.
Most rollers have a rotating shaft which turns in a stationary bearing housing at each end. Sometimes the shaft and roller are machined out of one piece of material. For cylindrical shell type rollers, short shafts are welded to plugs, which in turn are welded into the two roller ends. Assuming the bearing portion of such a shaft carries a uniformly distributed load (F) on a cantilevered beam of length (L), then its maximum bending moment is:
      M    max    =            F      *      L        2  and maximum shaft deflection:
      Δ    ⁢                  ⁢          y      max        =                    F        *                  L          3                            8        ⁢        E        ⁢                                  ⁢        I              .  